Tablets have been well known in the pharmaceutical industry since the late 19th century. Typically, a drug is mixed with inert ingredients (excipients) such as binders, fillers, antioxidants, etc., and compressed into solid dosage forms that are subsequently swallowed. Most of the excipients used in immediate release tablets are water soluble, since this increases the rate at which the tablet dissolves. Lipophilic substances are often incorporated into sustained release dosage forms in order to delay the rate at which the tablet dissolves.
Tablets have also been used as a means of providing single serving consumer items such as laundry soap, dishwashing detergents, etc. Like pharmaceuticals, most of the ingredients found in soap are either water soluble or are amphilic (i.e. soluble in both water and oil) and thus will dissolve quickly.
Tablets have also been evaluated in the food industry as a serving form. However, food scientists have run into hurdles that have limited the potential commercial applicability of such tablets. For example, European Application Number 0 572 138 describes attempts to make tablets for subsequent reconstitution as sugar free soft drinks. The '138 application describes the dilemma confronting these scientists. Tablets made using compression pressures typical in the pharmaceutical industry are poorly soluble in cold water. Decreasing the pressure used in compression enhanced solubility but lead to brittle tablets that broke during shipping. The solution to this problem, as described by the '138 application, is two fold. First, lipophilic substances such as magnesium stearate were omitted from the formulation. Fat inhibited dissolution of the tablets. Secondly, carbonates, or other salts capable of generating carbon dioxide were incorporated into the formulation. The generation of carbon dioxide promoted the physical disintegration of the tablet thereby promoting the dissolution of the beverage mix in cold water.
Food scientists have also attempted to produce tablets out of powdered milks. As described by U.S. Pat. No. 3,241,975, less than optimal results have been obtained. As described by the '975 patent at column 1, lines 15–25, milk powders compressed into tablets have unacceptable solubility, even in hot water. The solution proposed by the inventors of the '975 patent is to alter the content of the powdered milk. Specifically they propose incorporating from 3 to 4% by weight of alkali metal phosphates or alkali citrates. These salts enhance the solubility of the casein and ultimately the dispersibility of the powdered milk. Further, supplemental lactose is incorporated into the powdered milk to enhance its dissolution rate. This supplemental lactose can comprise up to approximately 25% of the tablet. Even with these significant modifications, the tablets require hot water to exhibit suitable dispersibility.
German Patent 29908880 describes a milk tablet that is soluble in hot beverages. The tablet contains whey protein, sugar and optionally egg whites. Such a composition is essentially fat free. The German patent teaches that fat should be omitted from these milk tablets in order to be readily soluble in water.
European Patent Application 1 048 216 also addresses the production of milk tablets. At column 1, lines 1–15, the '216 application points out that most milk tablets are made from skim milk. Skim milk is essentially fat free, having a maximum fat content of 1.5% w/w. Skim milk is used since tablets made from whole milk tend to produce solutions suffering from phase separation. Further, dissolution times are substantially increased as the fat content increases. The '216 application discusses the preparation of high fat tablets, but only exemplifies their dissolution in water having a temperature of 700° C.
Thus, while the prior art shows that food products have been prepared in tablet form, it also shows that a number of problems exist. First, tablets are typically only used to produce low fat foods. Secondly, even these low fat food will not dissolve in cool water in an acceptable time frame.
Infant formula is high in fat. Approximately 50% of the calories contained in infant formula are derived from fat. In a powdered product, this constitutes approximately 25% of the formula, based on weight. Thus, one would consider infant formula a poor candidate for tablet development. The high fat content suggests such tablets would not dissolve quickly. Rapid dissolution is especially critical for infant formula. Infants communicate their hunger by crying. Caregivers and parents want dosage forms that dissolve instantly, so that the crying may be dissipated. For example, powdered infant formulas dissolves in cool water within 15 to 60 seconds. Any product having a reconstitution time beyond that would be considered unacceptable to most consumers.